Heavy Truck Brake Adjustment-Problems And Solutions
Hank Seiff
ATA Foundation, Trucking Research Institute, USA
ABSTRACT
The National Transportation Safety Board recently
inspected 1,520 combination vehicles and found 56 percent
had brake violations serious enough to put the vehicles out
of service. The National Highway Traffic Safety Administration has said that brake performance could contribute to
as many as one-third of all truck crashes, although most
sources found 2 % or fewer truck crashes to be brake
related.
.. BACKGROUND
In its April, 1992, Heavy Vehicle Airbrake Performance
study [1], the National Transportation Safety Board (NTSB)
examined the brakes of 1,520 five-axle combination trucks
and found 56 percent had violations serious enough to be
placed out of service. Forty-six percent of all vehicles
inspected were placed out of service for out-of-adjustment
brakes alone.
Figure 1. State Police Inspector Measures Brake Adjustment
The NTSB study found that many motor carriers and
drivers of commercial vehicles fail to understand the need
for well-maintained brake systems. This lack of understanding is easy to comprehend - poorly-adjusted air-brake
systems give little driver "feedback" and in routine operations may perform adequately - but in emergency situations,
with high brake temperatures and hard applications, adequate braking may not be available.
While the number of brake violations found in roadside
inspections is high, there is no agreement on the contribution of those violations to truck accidents.
C:Qngr~ requested a study of the problem, suggesting
brake mechanic training praCticeS as the primary concern.
However, the Trucking Research Institute (TRI) and the
Federal Highway Administration (FHWA) agreed that mechanic training is likely to be only a part of the problem,
and broadened the study to a comprehensive effort to
identify cause(s) of brake violations and achieve solutions,
assuming that the problem's solution was likely to be some
combination of improved:
• Education and Information
• Equipment Technology
• Mechanic and Driver Training • Enforcement
• Management Commitment
The study concentrates on "solutions" to the brake
violation problem which are likely to be practical and
acceptable to the motor carrier industry. The assumption
is made that effective solutions to the brake violation
problem must, at least in the short term, accept the enforcement method and brake system which are presently in use.
The principal sources of information for the study were
a comprehensive literature search, interviews with a total of
51 motor carriers (almost equally divided between those
with low and high brake-violation rates in roadside inspections), interviews with truck manufacturers, brake suppliers, user groups and enforcement organizations, and a
review of FHWA's 1992 Motor Carrier Management
Information System (MCMIS) data.
The following findings, conclusions and recommendations represent the views of the author, who is responsible
for the accuracy of the data presented herein. They do not
necessarily reflect the official policy of the Federal Highway Administration.
Road transport technology-4. University of Michigan Transportation Research Institute, Ann Arbor, 1995.
575
ROAD TRANSPORT TECHNOLOGY-4
STUDY FINDINGS
CONTRIBUTION OF BRAKE VIOLATIONS TO TRUCK
ACCIDENTS
There are no good data and therefore no real agreement
on the contribution of brake violations to truck accidents.
Estimates range from zero (assuming "risk homeostasis"
[drivers adjust to improved brakes by increasing
speed/decreasing following distance so that risk level is
unchanged)) to 1 % COMC accident reports) to one/third [2]
of truck accidents being attributable, at least in part, to
brakes.
EFFECT OF ADJUSTMENT ON BRAKE EFFECTIVENESS
The vast majority of truck braking is done at low
decelerations, using low air pressures, with cool brakes.
With all brakes at the manufacturer's stroke adjustment
limit, a vehicle would provide acceptable stopping performance in normal (low deceleration, cool brakes) operation.
Because air brakes do not provide the pedal "feel" of a
hydraulic brake system, drivers may not be aware of brake
problems until the vehicle fails to perform properly in an
emergency (high deceleration; hot brakes) situation.
VEHICLES wrrn OUT-OF-SERVICE BRAKE VIOLATIONS
The National Transportation Safety Board placed 56 %
of a "representative sample" of 1,520 combination vehicles
inspected on the highway out of service for brake violations. Commercial Vehicle Safety Alliance (CVSA) inspections put a total of 21.1% of over S6,000 vehicles checked
(31.8% using the tougher level 1 inspections only) out of
service during Roadcheck 93.[3J MCSAP (Motor Carrier
Safety Assistance Program) inspections in 1990 put 18% of
the vehicles out-of-service for brakes.[4] There are a
number of reasons why these data are not directly comparable, but the same conclusion can be drawn from all of
them: there are too many trucks with brake violations
operating on the nation's highways.
STANDARDIZED ADJUSTMENT PROCEDURE
Standardized adjustment procedures (called for in the
NTSB report) for manual and automatic slack adjusters can
be found in The Maintenance Council's (TMC) Recommended Practice RP 609A, included in The Air Brake
Book.[S] These procedures are also found in recent video
training materials from TMCand the Owner-Operator
Independent Drivers Association. The procedures are
simple and direct. However they were not normally strictly
followed by the maintenance personnel visited during this
study.
AUTOMATIC SLACK ADJUSTERS
Various studies show the out-of-adjustment rate of
automatic slack adjuster (ASA) equipped brakes to be about
half that of brakes with manual slack adjusters (MSAs).
NTSB found that a fully-effective automatic brake adjusting
system would be the single most effective equipment
576
solution to the out-of-adjustment problem. Today's generation of ASAs are substantially improved over past ASAs,
but carriers report they are far from maintenance and
failure free. They can be installed incorrectly, require
frequent maintenance, and may fail in "dirty" carrier
operations. Many carriers visited during this study have
seen a major decrease in out-of-adjustment complaints and
maintenance requirements with ASAs. Others have tried
them and gone back to manual slack adjusters. Still others
have heard "through the grapevine" that ASAs are unacceptable in their type of operation. Often carriers are
unaware of the effectiveness of ASAs since they routinely
adjust (rather than check) both ASAs and MSAs at frequent
maintenance intervals.
NEW BRAKE TECHNOLOGY
In the not-too-distant past, wedge and disc brakes challenged the old, established S-cam drum brake for supremacy on heavy trucks. Neither design was widely accepted.
S-cam designs have been simplified over the years, and
have the advantages of availability and interchangeability of.
parts, mechanic understanding of the system, and low cost.
More importantly, they work well and are reasonably
accepting of mistreatment. In the near term we do not see
S-cams being displaced by other technology. In the longer
term today's air application system may be replaced by an
electro-pneumatic hybrid (Electronic Braking System [EBS]
or brake-by-wire) and disc brakes may again be considered
by the industry.
EXPERIENCE IN OTHER COUNTRIES
Other advanced countries have brake violation problems
similar to those found in the U.S. PMVI (periodic motor
vehicle inspection) requirements are more stringent in
Europe (and some Canadian provinces) than in the U.S.,
but it is not clear that there are differences in violation rates
attributable to these requirements. In U.K. "heavy goods
vehicle" PMVI inspections, the failure rate averages around
30 %, with the leading cause normally being brakes. The
British Vehicle Inspectorate's roadside inspections, which
include only a cursory visual inspection of brakes, put
7.2% out of service (1992/93) and gave 7.6% a "delayed
prohibition, " finding brake system components topping the
list of the most ireQ.uent defects. A trucking association
official in Europe summed up the general feeling of those
contacted for this study, saying "[tJruck brakes top the
failure list [in annual inspections], but no one recognizes it
as a serious problem. "
MOTOR CARRIER MANAGEMENT INFORMATION
SYSTEM (MCMIS) DATA
FHWA collects data on motor carrier operations,
inspections and maintenance. The 1992 data files used in
the study list 307,805 motor carriers and 1,129,672 vehicle
inspections. MCMIS data show a wide varia~on among
states in brake violations per vehicle inspection, ranging
from 1.9 in Maine to 0.12 in Illinois. Only part of this
variation is explained by different "levels" of inspections
run in different states. Nationwide, the most frequent
BRAKES AND ABS
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iii
single brake violation (44%) is "out of.adjustment." Yet
California, Michigan, New Jersey and New York record
less than 0.1 % brake violations as "out of adjustment. "
Those states apparently lump these violations in the "general" or "inoperative brakes" categories. In general, larger
fleets do have better vehicle and brake-violation ratios than
smaller fleets and newer vehicles are better than older ones.
See Figures 2 - 6, taken from 1992 MCMIS data.
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Figure 2. Brake Violation Rate by State
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Figure 3. Brake Violation Rate by Inspection Level
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""'ID
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Total
Figure 6. Brake Violation Rate by Vehicle Model Year
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Figure 4. Brake Violation Types - U.S. Total and New
York
CARRIER SURVEY AND ANALYSIS
Fifty-one carriers, almost equally divided between
those with very low and very high brake-violation ratios,
were visited. Although differences in such things as
mechanic training and hiring, shop cleanliness, and brake
inspection and adjustment practices were found, these
seemed to be subsidiary to two major differences: "type of
fleet cargo and operation," and "management commitment
to excellence" of the carriers. It is much harder for fleets
engaged in "dirty" (e.g. gravel, aggregate or mine opera-
577
ROAD TRANSPORT TECHNOLOGY-4
tions, [wood] chip hauling, container hauling) operations to
keep up good brake maintenance practices than for fleets in
"clean" (e.g. wholesale grocery distribution, gasoline,
general freight) operations. Management dedication to
good maintenance practices, can, but often does not,
overcome other fleet disadvantages.
MEETINGS WITH EXPERTS
Discussions with brake suppliers, tractor and trailer
manufacturers, motor carrier user groups, an enforcement
organization and brake repair facilities focused primarily on
the technical side of brakes and brake maintenance. Since
the 1973 oil embargo, effons to improve vehicle fuel
economy have led to greatly improved vehicle aerodynamics, lower rolling resistance, and smaller engines with less
internal friction. While doubling. fuel economy, this has
also doubled the amount of work brakes must do, by
decreasing a vehicle's natural retardation. During the same
period the maximum national gross vehicle weight increased
nine percent. All this with no increase in brake lining area
or brake drum size. The job of an automatic slack adjuster
is difficult because much of the available brake pushrod
travel is used for system deflection and drum thermal
expansion during hard brake applications, leaving the ASA
little tolerance to do its job. Brake system components
have been redesigned and lightened over the years to save
cost and weight. While lighter components are not necessarily weaker, they are generally less "stiff," allowing
greater deflection in hard brake applications.
CONCLUSIONS
THERE IS NO "SILVER BULLET"
The literature review, technical discussions, MCMIS
data study and meetings with low and high brake violationratio motor carriers make it clear there is no one simple
way to guarantee a quick and substantial improvement in
brake violation rate. Solutions such as educating and
informing carrier management and technical personnel or
better mechanic training will nOl stand by themselves.
Their success depends on each carrier's dedication to
vehicle maintenance excellence. Carrier dedication to
maintenance excellence often, bilt not always. follows from
an overall dedication to business excellence in all fields,
normally led by top management.
Although carriers are responsible for the safety of their
vehicles, not all companies will ever boast true management
excellence, and therefore not all carriers will fully meet
their responsibility. In our visits to 51 low and high brake
violation-rate carriers, it was clear that the type of business
in which a carrier is involved may make it relatively easy
or difficult to conduct an effective brake maintenance
program. Carriers in "dirty" operations have a much more
difficult time supporting good brake maintenance. Carriers
under strong time constraints at specific seasons (e.g.
serving road construction in the summer) have a difficult
time. And carriers in fiercely competitive fields (e.g.
hauling container chassis) may not feel they can afford the
time, or money or have the "clout· with shippers to assure
578
good maintenance. On the other hand, carriers hauling
"clean" commodities with trucks that return home at regular
intervals to company maintenance facilities. have an easier
time.
In even the worst case, there are management teams
that make vehicle maintenance a priority and succeed in
having low brake-violation rates. And in even the best
cases. some companies have poor mainteilance practices and
a high brake-violation rate.
Only providing more information and education about
brake problems will have little long-term effect on maintenance practices. Mechanic training can only be effective.
over the long term, in companies which strive for maintenance excellence. More/stronger enforcement is not likely
to prove cost-beneficial, however better targeted enforcement should be useful.
It appears that relatively straightforward technical solutions will provide the best substantial short-term improvement in the brake-violation rate. In the longer term. major
technical improvements will be made in truck brake systems
and brake inspection technologies.
The following matrix provides a quick overview of
potential short-term solutions to the brake violation problem. The information presented in the matrix is based on
the literature search and visits with brake system "experts"
and 51 motor carriers.
IT IS THE MOTOR CARRIERS' RESPONSIBILITY TO
PUT WELL-MAINTAINED, SAFE, VEHICLES ON THE
HIGHWAY AND OPERATE THEM IN A RESPONSIBLE AND SAFE MANNER
No matter how difficult it may be, because of equipment design, operational or financial pressures, staff
motivation or practical knowledge. motor carrier management is ultimately responsibility for the safety of its
vehicles and drivers.
AVAILABLE MCMIS DATA REPRESENT A SOURCE
OF INFORMATION FOR MOTOR CARRIER SAFETY
IMPROVEMENTS
MCMIS data provide a level of understanding of the
motor carrier industry, the enforcement community, and
motor carrier safety, which is not available elsewhere. The
MCMIS data in this report, concerned primarily with brake
violations, represent only a small percentage of what
appears to be available. The use of these data could be
expanded to help understand the industry and to achieve
maximum results from the federal and state enforcement
programs. In-depth study and time-series evaluations can
track the effectiveness of regulatory changes (e.g. introduction of the CDL, ASAs or ABS), and the relationship
among company variables (e.g. size, type of operation,
location, age of equipment, hours of service, accident type
and severity). The already-available data can provide
higher levels of motor carrier safety without necessarily
increasing regulatory burdens or enforcement costs. To be
most effective, vehicle identification number (VIN) should
be recorded for each vehicle inspected.
BRAKES AND ABS
Suggested Solution
Upside
Likelihood of Implementation
Downside
Weekly brake
adjustment
Almost perfect solution
Costly, time consuming
Few carriers can be expected to do this religiously
Mcchanic training
Better quality maintenance
Costly, time consuming
Effectiveness depends on management commitment to excellence
Management information
Greater quality and quantity of
maintenance
Costly, time consuming
Could be implemented on reasonable level
by FHWA, ATA, TMC. Targeted program
most cost!effective.
More enforcement
More carrier management concern for brake maintenance
Costly, time consuming
Significant resources required
More targeted enforcement
Aimed at carriers with known
problems
Slight additional cost
Demonstration could be run under Phase
of this program
Annual or semiannual state or
federal inspection
(European style)
Vehicles will be completely
checked out at least once or
twice a year
Costly, time consuming
Significant resources required. Carrier
opposition likely.
Present ASAs
> 50% improvement in adjustment
Less frequent brake inspection, increased cost and complexity compared w
MSAs
Required on all new air brake vehicles
10/94. FHWA NPRM considering requiring continued use and retrofitting.
Only a matter of time and demand
n
Best short-term technical solu-
Less frequent brake inspection. De-
tion
signs not prese:ntly in place.
Less frequent and less sensitive
adjustment. Improved fade
resistance and high temperature
performance.
May s/igbtly increase air consumption
and cost. Need changes in FMVSS 121
brake reservoir requirements.
Retarders
Decrease load on brake system
and frequency of adjustment
Substantial cost penalty, increased
weight and maintenance
Continued slow increase in use rate
Air discs
Less temperature sensitivity,
less system deflection
Major changeover in industIy. Possible
incompatibilities. Higher cost. Systems
not presently in place. Need to agree
on inspection requirements.
Long term good bet, but not until systems
proven acceptable, perhaps in Europe
Stiffer components
Less system deflection
Increased cost, weight
Possible if ASAs and long-stroke chambers
not adequate
Pushrod marking
Spocing out-of-adjuStment
brakes somewhat easier
Checking brake adjustment still aWkward
Required on all new air-braked vehicles
10/94
Good brake out-ofadjustment/failure
sensor
Driver feedback of brake system
problem
Cost, complexity of present systems
Likely only as benefit of future EBS unless
simple, low-cost, low-maintenance new design developed
Pun:hased maintenance
Potential for better quality maintenance
No assurance of universal good quality.
Lack of carrier control.
Will likely increase in use over time as
found costlbeneficial to carriers and equipment and regulations become more complex
CVSA, TMC
program to work w
fleets on inspection
requirements
Better quality maintenance
Cost, likelihood that problem carriers
will sbow no interest
Demonstration could be run under Phase n
of project
Improved ASAs
Long-stroke chambers
.-
V r:ry likely
-
Figure 7. Brake Violation Solution Matrix
579
ROAD lRANSPORT TECHNOLOGY-4
IN THE SHORT 1ERM, OVERALL TRUCK BRAKE
SYSTEM DESIGN WILL CHANGE VERY LITTLE
The basic design of today's air-actuated, cam-operated,
drum brake system has changed little in the past 70 or so
years. It has survived challenges from wedge and air disc
brakes in the past 30 years, and will likely be challenged
(and may be overcome) by an electronically operated and
controlled, air-actuated, disc brake system in the future, but
not the near future.
clearly necessary to achieve the type of reliability found in
other truck components.
The environment in which an ASA operates makes its
job extremely difficult. Much of the available pushrod
movement is taken up by system deflection in the extremely
high-pressure brake application used to check brakes in
roadside inspections (or in a high-deceleration stop). Hard
or continuous brake application raises temperatures causing
drums to expand, using more pushrod travel. This leaves
Figure 8. 1921 Mack chain drive brake actuation system was similar in principle to today's cam-activated drum brakes
(although it used mechanical, not pneumatic, power)
580
Truck manufacturers and operators look for a number
of things in designing and specifying a brake system and
brake components:
• Effectiveness
• Durability
• Low initial cost
• Low maintenance cost
• Simplicity
• Standardization
• Parts availability
• Balance and compatibility
• Regulatory compliance • Light weight
Today's S-cam air brake systems meet all these
requirements, to one degree or another, and mechanics are
experienced in maintaining them. .The principal reasons for
considering a major brake system redesign would be to
achieve higher effectiveness (e.g. greater energy absorption), better durability and/or better balance and compatibility. Today's systems enjoy the benefits oflow initial cost,
simplicity, standardization and widespread parts availability.
a small operating envelope for ASAs to keep the system
within legal limits, and this envelope gets smaller as system
components wear.
Some ASA suppliers and vehicle OEMs feel ASAs
alone can virtually eliminate out-of-adjustment violations.
Others feel that ASAs, in combination with long-stroke
chambers, are needed. They are ready to provide longstroke chambers as standard equipment if FMVSS 12l's
brake reservoir capacity requirements are changed to
accommodate them.
Long-stroke chambers should make (he job of any ASA
easier. NTSB concluded that •... combining a properly
installed and maintained automatic slack adjuster with a
long stroke chamber could reduce the percentage of brakes
at or past the limit of adjustment from ... 26-percent.... for ... manual slackadjusters ... to ... 4-percent.... " [1]
IN THE SHORT 1ERM, NEAR UNIVERSAL USE OF
IMPROVED ASAs AND LONG-STROKE CHAMBERS
OFFERS THE SINGLE BEST SOLUTION
Past automatic slack adjuster equipped vehicles have
had about half the brake out-of-adjustmem violations of
vehicles with manual slacks. Each succeeding generation
of ASA design is found to be more reliable. But users say
today's ASAs still may be installed incorrectly and require
continuing maintenance (primarily greasing) and checking
to be sure they operate properly. Further improvements are
THE TRUCKING INDUSTRY SHOULD STRIVE FOR A
BRAKE SYS1EM AS MAINTENANCE AND FAILUREFREE AS OTHER MAJOR TRUCK SYS1EMS
Excellent self-adjusanent systems have been in place on
light-duty vehicles since the early '60s. Certainly trucks
are asked to operate under more difficult circumstances than
most passenger cars, but less maintenance-intensive brake
systems are a reachable goal. Truck engines, transmissions, drive trains and body hardware require far less
maintenance than equivalent passenger-car systems, while
BRAKES AND ABS
operating in a more difficult environment - wby not brake
systems?
Automatic slack adjusters are a good start. Today they
provide a major decrease in brake adjustment violations.
Still, today's ASAs are not as maintenance and failure-free
as users have come to expect of most truck components.
The best of today's technology can provide far more
maintenance and adjustment-free brake systems.
A SIMPLE, LOW COST, LOW MAINTENANCE,
SYSTEM PROVIDING DRIVER FEEDBACK OF BRAKE
CONDmON WOULD DECREASE THE FREQUENCY
OF BRAKE VIOLATIONS
While measuring adjustment (and adjusting) air brakes
is not difficult, it ~ time consuming and messy, since it
requires getting under the vehicle. This is contrasted with
the simplicity of monitoring brake adjustment in a bydraulically-operated brake system. where the driver feels the
pedal go down further if brakes are not properly adjusted.
Various methods have been developed to ease the task
of cbecking brake adjustment, from the simple pusbrod
marking now required by FMVSS 121, to sophisticated
electronic brake-adjustment sensing and reporting systems.
None of these systems fully meets industry needs to provide
a simple, low-cost, low-maintenance, driver feedback
system.
The benefits of a simple, low-cost, low-maintenance
'system to provide driver ~back or. a brake failure
warning could be substantial and should not necessarily
await major brake system redesigns.
MECHANIC AND DRIVER TRAINING ARE NOT
STAND-ALONE SOLUTIONS TO THE BRAKE VIOLATION PROBLEM
Any lack of mechanic and/or driver training in brake
maintenance is a symptom of the problem, not the problem
itself. While it is true that there is no standardization
among carriers and carrier mechanics on methods of
cbecking and adjusting brakes, there appears to be adequate
material and tutelage available from brake suppliers, vehicle
manufacturers, and carrier organizations sucb as The
Maintenance Council. However, many carriers are not
aware of the availability of this information or do not take
advantage of it.
The real issue is management interest in and commitment to proper maintenance practices. Some carriers in socalled "dirty" operations exhibit excellent maintenance
practices and some in so-called "clean" operations have
poor brake maintenance. Improved mechanic and/or driver
maintenance performance follow from a management
commitment to maintenance excellence, not simply from the
creation and distribution of more or better training materials.
Brake adjustment is a relatively simple procedure.
Some companies require or encourage drivers to adjust
brakes. Some forbid drivers to adjust brakes. It is likely
some good could come from more people - drivers,
mechanics and management - understanding brake systems
and their needs, and making repairs and adjustments as
necessary. A low-cost government/industry program could
target carriers with brake-maintenance problems to receive
specific guidance (e.g. TMC's brake video and recommended practices) and widely distribute leaflets on proper brake
adjustment and maintenance. But the significant resources
involved in an across-the-board mechanic training activity
would likely not be cost/effective.
EFFORTS TO IMPROVE MANAGEMENT COMMITMENT TO BRAKE MAINTENANCE EXCELLENCE
CAN BE MOST COSTIEFFECTIVE USING A TARGETED APPROACH, RATHER THAN MAJOR ACROSSTHE-BOARD PROGRAMS
With or without improvements in brake system technology, management commitment to maintenance excellence
can substantially lower the level of motor carrier brake
violations.
In most cases, a company's vehicle maintenance
policies flow from the attitudes of top management. Top
management (like the rest of us) can be influenced and
encouraged to act in a conscientious way by peer pressure,
law and regulation, morality, education, (bad or good)
press, profits, and enforcement (coercion).
The number of vehicle inspections has increased from
perhaps thirty to thirty-five thousand a year in the early
'60s to two million a year today without eliminating the
brake-violation problem. Most carriers visited during the
study understand the nature and importance of the problem,
believe they are doing a good job on brake maintenance and
feel it is someone else wbo has the bad record. Based on
tb.ese visits. it appears that one solution may be a targeted
education program, aimed at a relatively small number of
carriers with known higb brake-violation rates.
The use of MCMIS data allows the identification of
carriers with higb brake-violation rates. A targeted education program could send personal letters to those carriers,
reminding them of the brake violation problem, citing
figures showing that they are a major cause of the problem.
and offering belp from industry sources, trade associations
or state or regional motor carrier safety personnel. Limiting the program only to the 10% of carriers with over 25
inspections in the past year, with the highest-violation rate,
would include less than 800 carriers, a workable number.
but with potential for substantial results.
A SIMPLE, STANDARDIZED, MORE ACCURATE
TOOL WOULD BE USEFUL FOR INSPECTORS IN
MEASURING BRAKE PUSHROD TRAVEL
During this study a number of carriers and others
expressed concern with the accuracy of brake adjustment
measurements taken by some inspectors.
The width of the cbalk lines often used by inspectors to
mark the pusbrod may introduce error. Inspectors commonly measure to the nearest eigbth incb, rather than being
more exact. Inspectors may have trouble subtracting
fractions of an incb (e.g. 5 5/8" minus 3 15/16") in their
beads while lying on their backs under wet trucks in semidarkness.
To assure more accurate and repeatable measurements,
a simple tool should be developeQ for use in cbecking brake
adjustment. It migbt, for example, use a magnet to stick
against the brake chamber face and have a sliding scale
with a book to snap onto the clevis end of the pusbrod. The
•
581
ROAD TRANSPORT TECHNOLOGY-4
starting with a program of contacting high violation-rate
carriers, informing them of their problems, and offering
them both help from indUStry and government sources
(carrot) and selective enforcement (stick) as necessary.
6. The use of MCMIS data should be expanded to
help understand the indUStry, and achieve maximum results
from federal and state enforcement programs.
7. Vehicle Identification Number (VIN) should be
recorded and reported for every vehicle inspection.
8. A simple, standardized, more accurate tool should
be developed for use by inspectors in measuring brake
pushrod travel.
REFERENCES
1. National Transportation Safety Board, Heavy Vehicle
Airbrake Performance, NTSB/SS-92-01, April 29,1992.
Figure 9. Some carriers use a "stock box" system to
provide all necessary pans for replacement during brake
relining
sliding scale would be set at "0" with brakes released. The
inspector would install the measuring devices at each wheel,
come out from under the truck to (or have a co-worker)
monitor a proper brake application by the driver, and then
get under again to read the total travel on each tool. A
more sophisticated version could even provide a digital
readout for increased accuracy and ease of use.
RECO:MMENDATIONS
1. Motor Carriers must accept the ultimate responsibility for appropriate maintenance to ensure the safety of
their vehicles.
2. A vehicle demonstration program, incorporating
the best current technology (e.g. ASAs, long-stroke
chambers and low-deflection components) to provide a
nearly "no adjust, no maintenance" brake system, should be
undertaken to encourage the industry to produce and accept
this technology.
3. Brake suppliers and/or vehicle OEMs should strive
to develop and market a simple, low cost, low maintenance,
system to provide driver feedback of brake failure (particularly out-of-adjustment brakes).
4. Mechanic and driver training should not be seen as
a stand-alone solution to the brake violation problem.
5. Government and industry efforts to improve motor
carrier management commitment to brake maintenance
should take a targeted, rather than a general approach,
582
2. Clarke, Radlinski, and Knipling, Improved Brake
Systems for Commercial Motor Vehicles, NHTSA, DOT
HS 807 706, April 1991.
3. Commercial Vehicle Safety Alliance, Report of Roadcheck 93 Activities, Prepared by FHWA, OMC, September
1993.
4. Heusser, Ronald B., "Air Brake Inspections on FiveAxle Combinations, " SAE Paper 922443, November, 1992.
5. Commercial Carrier Journal, The Air Brake Book, 1992.